Vitamin b6 intermediate



Patented 2, 1943 UNITED STATES PATENT OFFICE vlramnri lzflz nmnm'rn Gustaf B. Carlson, Pearl River, N. Y., asslgnor to Lederle Laboratories, Inc., New York,'N. Y..- a corporation of Delaware T Serial No. 412,431

60lalms.

This invention relates to new chemical compounds and more particularly relates to an intermediate for usein the preparation of vitamin B6 and to a process of preparing the same.

The compounds which 1 have found to be use ful as a vitamin Be intermediate are those represented by the following iormula:

N CN on L1: N

' in which Xrepresents chlorine or bromine.

The reactions which take place in my process may be represented as follows:

'Ihe'invention will be illustrated in more detail in conjunction with the following specific exam-1 pies.

Preparation of the amide of 3-cyano-4-carboxy? 6-meth1 l' pilridone-Z Two hundred grams of the ethyl ester of 3-0)" ano-4-carboxy-6-methyl pyridone-2 (prepared according to the method described by Bardhan, J. C. S., 2223 (1929)) were added to 3.5 liters of absolute methanol saturated at 0 C. with gaseous ammonia and, after 7 days at 0 0., the filtered solution was concentratedin vacuo to a small volume to give the amide of 3-cyano-4- carboxy-6-methyl pyridone-z, which melted above 300 C. with decomposition. The compound so prepared is useful as an intermediate in the synthesis of vitamin Be.

In the foregoing specific example the ethyl ester oi 3-cyano-4-carboxy ii-methyl pyr1done-2 was employed in carrying out the reaction and is the preferred ester because of its cheapness and availability. It should be understood, however, that the ethyl ester may be replaced by other suitable esters of 3-cyano-4-carboxy-6- methyl pyridone-2. Among the Various esters that may be employed are the alkyl esters such as methyl, propyl amyl, hexyl, and the like. The aromatic esters, such as phenyl and naphthyl. may similarly be employed.- Esters of the aralkyl type which may be satisfactory are those such as, the benzyl ester and the ester of 2-hydroxymethyl naphthalene, cinnamyl alcohol, etc. The esters derived from cycloaliphatic alcohols such as cyclohexanol, methyl cyclohexanol, fenchol or fenchyl alcohol, and the like, may be employed. The use of the various other esters such as those derived from heterocyclic alcohols, for example 2-methyl-1-propanol are not precluded from the present invention. Preparation of 3,4-\dicyano-6-methyl pyridone-Z Dehydration of the amide of 3-cyano-4-carboxy-fi-methyl pyridone-2 was effected by treatment with phosphorous oxychloride, both without the use of a solvent and in hot toluene solution. The details of a typical experiment in which no solvent was used are given herewith. The amide (2 g.) and 25 cc. of phosphorous o ychloride were heated in a bath at 145-150 C. r

for 50 minutes, excess phosphorous oxychloride was distilled in vacuo and the residue was treated with 50 g. of cracked ice. The crystalline product was filtered of! and recrystallized from aqueous alcohol. The pure dinitrile (0.4 g.) melted at 241-243" C. (uncorrected).

In subsequent experiments it was found to be advantageous to employ an inert diluent in the reaction mixture and typical of such a dehydration are the following details. A mechanically stirred mixture of 50 g. of the amide, 250 cc. of dry toluene and 250 cc. of phosphorous oxychloricle was heated in a bath at -133 C. for 9.5 hours and, after 15 hours at room temperature,

the undissolved material was filtered oil and thoroughly extracted with toluene and ether. The solid was then extracted with acetone and yielded 8.9 g. of unchanged amide. The original toluene filtrate and the combined toluene and ether extracts were evaporated in vacuo and the residual product was treated with 20 cc. of ice water. The crude yellow mixture was diluted with 800 cc. of hot acetone, the insoluble product was filtered oil, twice extracted with 300 cc. of hot acetone, and yielded 11.3 g. of recovered amide. The aqueous acetone filtrate and the combined acetone extracts were concentrated in halogenating the pyridone, but it should be understood, that other suitable halogenating reagents may be used instead, for example phosphorous pentabromide. Similarly. the 2-chloro compound is the preferred intermediate for use in the synthesis of vitamin Be since it is somevacuo to a small volume and yielded 13.4 g. of the Preparation of 3.4-dicz/ano-5-nitro-6-methyl mlridone-z A suspension of 3,4-dicyano-6-methyl pyridone-2 (3.8 g.) in 20 cc. of acetic anhydride was treated at 45-52" C. with a solution prepared from 3 cc. of fuming nitric acid, 3 cc. of acetic anhydride and a few crystals of urea. The resulting solution was poured onto cracked ice and yielded 2.6 g. of the crude nitro compound. The solid was dissolved in 75 cc. of acetone, the solution was treated with active charcoal and the filtered solution was concentrated in vacuo to a small volume. The solution was rapidly diluted with ether and the precipitated product was recrystallized from an acetone-ether solution. The pure nitro derivative (1.6 g.) which was obtained had a melting point of 242-244 C. uncorrected.

Preparation of 2-chloro-3,4-dicz/ano-S-nitro-B- methyl pyridin crude chloro compound. After recrystallizatiom;

4.3 g. of the pure product was obtained which melted at 86-86.5 C. uncorrected.

I prefer to use phosphorous pentachloride for" what cheaper and more easily handled than the corresponding 2-bromo derivative. It should be understood, however, that the z-bromo compound may be satisfactorily used to replace the 2-chloro compound in the synthesis of vitamin I claim:

1. The process which comprises halogenating 3,4-dicyano-5-nitro-G-methyl pyridone-2 to form 2-halo-3,4-dicyano-5-nitro-6-methyl pyridin.

2. The method of preparing 2-chloro-3,4-dicyano-5-nitro-6-methyl Dy idin which comprises reacting 3.4-dicyano-5-nitro-6-methyl pyridone-2 with phosphorous pentachloride.

3. The method of preparing 2-bromo-3,4-dicyano-5-nitro-6-methyl pyridin which comprises reacting 3,4-dicyano-5-nitro-6-methyl pyridone-2 with phosphorous pentabromide.

4. The compounds of the formula:

NO ON in which X is a member of the of chlorine and bromine.

5. The compound of the formula:

group consisting NO ON GUSTAF H. CARLSON. 

